Final answer:
The correct option (A). A pinnacle is a subordinate vertical structure used in Gothic architecture to add weight to buttress piers, enhancing the function of flying buttresses by transferring weight loads from upper stories and vaults to the ground.
Step-by-step explanation:
In Gothic architecture, the subordinate vertical structure that terminates in a pyramid or spire and is used to add weight to a buttress pier is known as a pinnacle. This element is instrumental in enhancing the function of flying buttresses, which are exterior structural supports that transfer the thrust of a building's vault over to external supports. Flying buttresses, originating during the Gothic period, allowed for higher, thinner walls and the inclusion of large stained glass windows by redirecting the weight and lateral thrust away from the walls and into the ground.
The pinnacle, commonly found atop flying buttresses, not only served a structural purpose by adding weight but also decorated the skyline of cathedrals with their graceful, upward-soaring forms. They often appeared in alternation with gables, contributing to the ornate aesthetic that is characteristic of Gothic architecture. The use of these architectural techniques allowed the Gothic style to achieve unprecedented heights and intricate designs in the cathedrals of Europe, revolutionizing the way structures were built during that time.